Chicago's Willis (formerly "Sears") Tower is one of the tallest skyscrapers in the world — and yesterday it was scaled by amputee/bionic-badass Zac Vawter.

Vawter had assistance, of course, albeit in a truly revolutionary form. In a bioengineering first, the 31-year-old — who lost his right leg in a 2009 motorcycle accident — scaled all 103 of the building's floors with the aid of what researchers call the world's first neural-controlled bionic leg.

Lead researcher Levi Hargrove told The Chicago Tribune the prosthesis works by responding to electrical signals given off by muscles in Vawter's upper legs, "where the surgeon who amputated his leg reattached the dangling nerves that previously carried signals past his knee":

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The procedure, known as targeted muscle reinnervation, allowed Hargrove and his team at the [Rehabilitation Institute of Chicago's] Center for Bionic Medicine to tap into the preserved neural signals to control the prosthetic limb.

"He just thinks about moving his ankle," Hargrove said as an example. "He thinks about doing those movements and the signals travel down the nerves and are redirected onto hamstring muscle. The body doesn't know that the ankle is not contracting. It is very intuitive for him."

What's really mind blowing is how quickly Vawter managed to scale the tower. For a healthy, fully-intact person, the average stair-climb at Willis Tower (all 2,109 steps of it) takes upwards of thirty minutes. Vawter did it in 45, beating out plenty of other four-limbed climbers participating in Sunday's annual SkyRise Chicago Tower Climb — not bad at all for the world's first neurally controlled crural prosthesis.

"We were testing the leg under extreme conditions," said Joanne Smith, the Rehabilitation Institute's CEO, in a statement. "Very few patients who will use the leg in the future will be using it for this purpose. From that perspective, its performance was beyond measure."